Driving mechanism for a load with inertia

ABSTRACT

In a tape player, the load including the flywheel has an inertia which is greater than that which a small synchronous motor for operating the player can overcome upon initial energization. To permit use of such a motor, a slip torque clutch is connected between the flywheel and the motor to provide gradual acceleration and rotation of the flywheel at reduced torque requirements for the motor.

United States Patent [191 Noguchi DRIVING MECHANISM FOR A LOAD WITH INERTIA [75] Inventor: Masaru Noguchi, Tokyo, Japan [73] Assignee: Alps Motorola, Inc., Tokyo, Japan [22] Filed: Mar. 21, 1973 [21] Appl. No.: 343,353

[52 US. Cl. 64/27 s, 64/30 E [51] Int. Cl. Fl6d 3/14 [58] Field of Search 64/30 E, 30 R, 30 D, 30 C, 64/29, 15, 27 S [56] References Cited UNITED STATES PATENTS 1,535,639 4/1925 Weber 64/27 S 2,595,454 5/1962 Greenlee 64/30 E 2,907,190 10/1959 Pastor 64/30 D OTHER PUBLICATIONS Publication IBM Technical Disclosure Bulletin Drag Clutch by R. Laybourn, Vol. 15, No. 3, Aug..l972.

Primary Examiner-Samuel Scott Assistant Examiner-Frank H. McKenzie, Jr. Attorney, Agent, or Firm-Mueller, Aichele & Ptak [5 7] ABSTRACT In a tape player, the load including the flywheel has an inertia which is greater than that which a small synchronous motor for operating the player can overcome upon initial energization. To permit use of such a motor, a slip torque clutch is connected between the flywheel and the motor to provide gradual acceleration and rotation of the flywheel at reduced torque requirements for the motor.

4 Claims, 14 Drawing Figures 3,851,499 Dec. 3, 1974 PATENILBEL' am TORQUE TORQUE -I- FIG. 5

TORQUE -9- MOTOR COUPLING CLUTCH FLYWHEEL H I! 0, 0 Q 2 f m 1 F 2 o v g A 8 fin a c 'J"*"*" LOAD mum 31914 3.851.499 suwaur 3 MOVEMENT PATENTEL 3,851,498

SHEET BM 3 FIG. /3

COUPLING v FLY WHEEL DRIVING MECHANISM FOR A LOAD WITH INERTIA BACKGROUND OF THE INVENTION In the past, the mechanisms for tape players, disc record players, etc., having high inertia required a DC motor, an induction motor, or a hysteresis synchronous motor as the driving element. These motors, however, are rather expensive and have been an obstacle to a reduction in the cost of the tape player device as a whole. In addition to these motors, synchronous motors are available. Synchronous motors have superior performance as to efficiency, speed stability, and they are rela tively inexpensive compared to other types of motors. Synchronous motors, however, produce little output torque at other than the synchronous speed of operation which makes self-starting of motors of this type almost impossible when they are connected to a high inertia load, such as exists in tape players and the like. As a consequence, synchronous motors have not been used as the drive motor for tape players.

I It is desirable to obtain the advantages of the superior performance of a synchronous motor in a tape player device.

SUMMARY OF THE INVENTION It is an object of this invention to use a synchronous motor to drive a high inertia load.

It is another object of this invention to use a synchronous motor in a tape player to drive the flywheel and load of such a tape player.

It is a further object of this invention to employ a slip torque clutch between a synchronous motor and a high inertia load to permit utilization of a synchronous motor for driving such a load.

In accordance with the preferred embodiment of this invention, a synchronous motor is used as the driving motor for a-tape recorder load. The load of the recorder has an inertia which is great enough that the synchronous motor alone would be incapable of providing acceleration and rotation, so that a coupling apparatus including a slip torque clutch interconnects the motor and the load and limits the torque applied to the load by the motor to an amount sufficient to enable start up of the motor upon initial energization.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a graph of the torque versus time required to rotate and accelerate an object having inertia; FIG. 2 is a block diagram of the output transmittal steps of an ordinary motor coupled to a load;

FIG. 3 is a drawing of a torque versus time for the arrangement of FIG. 2;

FIG. 4 is a graph of torque versus time for a synchronous motor coupled as shown in FIG. 2;

FIG. 5 is a block diagram of the output transmittal steps of a synchronous motor coupled in accordance with a preferred embodiment of this invention;

FIG. 6 shows the operating characteristics for the coupling of FIG. 5;

FIGS. 7, 8 and 9 illustrate a clutch device useful with the preferred embodiment of this invention;

FIG. 10 is a graph of torque versus movement for the clutch device ofFIGS. 7, 8 and 9;

FIGS. 11 and 12 illustrate operating arrangements of FIG. 13 is a block diagram of another embodiment of the interconnections of a motor and load; and

FIG. 14 is a perspective view of components arranged in accordance with the block diagram of FIG. 13.

DETAILED DESCRIPTION torque required to accelerate and rotate an object having inertia reduces gradually. In FIG. 2 a motor is shown coupled to a load through a flywheel with the aid of a coupling device with each of these components being shown as a block. The torque to be supplied out of the coupling device is symbolized as Q, underneath the block for that device in FIG. 2. Similarly, the torque required to accelerate the flywheel is shown as Q and the torque necessary for constant rotation of the load is shown as Q A plot of torque with respect to time to accelerate a load to an operating speed is shown in the solid line in FIG. 3. The time S is the time required before the flywheel attains the number of rotations of the motor operating speed. Then the constant torque O is required for steady rotation of the load. This torque O is reached with a gradual reduction in the initial torque 0 shown in FIG. 3.

In general, the pull-in torque required for starting a synchronous motor from its stationary state, that is to make it attain the number of synchronous rotations by acceleration and into the number of rotations required for synchronous operation, is obtained by energy from outside the motor, self-perturbation or vibration. Usually the time for attaining such a number of rotations is a very short period which is equal to one-half or one cycle of the synchronous frequency of the synchronous motor. As a consequence, an exceedingly large rating in the initial torque is required for such a motor when it is used as the drive motor of a tape player provided with load components having inertia. For example, as shown in FIG. 4, a much larger rating of the initial torque Q, than the torque Q necessary for the load is required. This, in the past, resulted in the necessity of providing a much larger motor than necessary for thesteady state operation, simply to enable initial acceleration of the flywheel into synchronous operation. For this reason, synchronous motors have not been used as t the drive motors for tape players.

In accordance with a preferred embodiment of this invention, a synchronous motor is used as the driving prescribed rating is delivered to the motor, the clutch the interconnections illustrated in block form in FIG.

slips to limit the load placed on the motor. The flywheel then is turned gradually until it obtains the full pull-in torque at the synchronous speed of the motor. This permits the use of a much smaller synchronous motor than is possible without the use of the slip torque clutch.

Referring to FIG. 5, there is shown an embodiment in block diagram form of this device. FIG. 5 shows the fundamental construction which consists of a synchronous motor coupled through a coupling to a slip torque clutch connected to a flywheel, with the flywheel coupled to a load. The torque supplied out of the coupling device is indicated as Q," in FIG. 5, with the torque from the clutch being indicated as Q The torque necessary for the flywheel is Q and finally the torque required to cause steady rotation of the load is Q The variation of the motor torque over a period of time is illustrated in the solid line in FIG. 6. The torque transmitted to the flywheel is limited to the rating of Q, in FIG. 6, since this is the torque at which the slip torque clutch begins to slip. As a consequence, the starting torque for the motor also is 0,, that is Q," is equal to 0,. This is sufficient to enable starting of the motor, and the total torque applied to the flywheel during its accelerating period then is the same torque Q Thus, as shown in FIG. 6, between the points A and B, the torque Q, is transmitted to the flywheel by the clutch and the flywheel is gradually accelerated. When the flywheel reaches the desired velocity at point B, slip on the slip torque clutch ceases; and the torque necessary for acceleration of the flywheel decreases to the point C where the torque is required for continuous rotation of the load at the point in time At this point, the motor is operating at its synchronous revolutions.

Superimposedv on the solid line curve of FIG. 6, which has just been described, there is a dotted line curve corresponding to that of FIG. 4 to show the torque required when the synchronous motor and the flywheel are directly joined together. It is obvious by comparison of these two curves that while the motor and the flywheel are in direct connection, acceleration can be performed in a short period of time S', but an exceedingly large starting torque Q, is required. When the slip torque clutch is interposed between the motor and the flywheel according to this invention, the period for acceleration of the flywheel is lengthened to time S, but the initial torque Q," required from the motor is much lower than the torque Q,'. The time required to accelerate the flywheel to operating speed in actual use can be determined by varying the adjustments of the slip torque clutch to determine the torque Q, at which the clutch will slip.

A clutch which is suitable for coupling the motor to the flywheel is shown in FIGS. 7, 8 and 9. This clutch is of small size, is of relatively simple construction and can be manufactured inexpensively. The clutch also works bidirectionally which is a desirable feature for use in a tape player.

In the clutch shown in FIGS. 7, 8 and 9, the drive shaft 1 is connected to the motor or driving source and a hollow cylindrical clutch drum 2 is secured to the drive shaft for rotation with it. An arcuately shaped clutch spring 3 with the proper elasticity is pressed upon the inner surface of the clutch drum and expands against the inner surface of the drum. A driven shaft 4 of a flywheel for coupling a load has a pair of levers 5 firmly attached about it, and the portion carrying the levers 5 is located inside the clutch drum cylinder in a position to permit the levers 5 to engage projections 6 which are bent inwardly from the ends of the arcuate spring 3. The shafts 1 and 4 are aligned with one another.

When the driving shaft 1 is turned in the direction of the arrow 7, shown in FIGS. 8 and 9, the clutch drum 2 also rotates in the same direction. As a consequence, the clutch spring 3, firmly pressed upon the clutch drum, also is rotated in the same direction. Then the contact 6 for the lever provided on the clutch spring 3 hooks the shoulder C on the lever 5, as shown in FIG. 8, which results in the rotation of the drive shaft 1 transmitted to the driven shaft 4 through the spring 3.

When a load in excess of a given amount is added to the drive shaft 4, the side A of the clutch spring 3 begins to slip; and on the other side B, the clutch spring is pushed inwardly as shown in FIG. 9 to rotate toward the direction of the arrow 7 by the friction produced between the clutch drum 2 and the spring 3. This causes a space to appear between the clutch drum 2 and the clutch spring 3 as shown in FIG. 9. Accordingly, the friction between the clutch spring 3 and the drum 2 is reduced and the drum 2 slides relative to the spring 3. Thus the transmittal of rotation from the driving shaft 1 to the driven shaft 4 is limited to the torque at which the spring 3 commences slipping relative to the clutch drum 2.

The clutch spring 3 has sufficient elasticity to make close contact with the clutch drum 2 and requires force to open it inwardly toward the axis of the drum. When no slip occurs, all of the force transmitted by the drive shaft 1 is coupled to the output shaft 4. The torque delivered to the driven shaft 4 is limited, and the range of this limited torque is proportional to the strength of the spring 3 which tends to expand it outwardly into engagement with the inner surface of the clutch drum 2. Thus, by varying the characteristics of the clutch spring 3, it is possible to vary the limited torque which is transmitted from the drive shaft 1 to the driven shaft 4. Ac- I cordingly, the clutch is of such construction that the time S for acceleration can be adjusted.

Although in the above explanation it has been indicated that the motor is connected to the shaft 1 and the load or flywheel is connected to the shaft 4, the same result can be acquired with these being connected in reverse.

FIG. 10 illustrates movement of the driven shaft 4 versus the torque applied by the driving shaft 1 through the slip torque clutch shown in FIGS. 7, 8 and 9.

FIGS. 11 and 12 illustrate portions of a tape player with the motor, flywheel, load, and clutch interconnected in accordance with the block diagram of FIG. 5. In FIGS. 11 and 12, the synchronous motor M is coupled by a coupling device G to the slip torque clutch C, which may be of the type illustrated in FIGS. 7, 8 and 9. The torque clutch C then is coupled to a flywheel I, the shaft of which comprises the capstan shaft Ca for driving a tape T against pinch roller P. It should be noted that in both FIGS. 11 and 12, the clutch C is interposed between the motor M and the flywheel I, although two different forrns of drive between the motor M and the flywheel I are illustrated. The basic operation, however, is the same for both embodiments.

FIG. 13 illustrates a block diagram in which the load is shown coupled to the motor output in parallel with the coupling of the clutch to the flywheel. FIG. 14 illustrates the manner inwhich the block diagram connections in FIG. 13 are realized in a tape player. In FIG. 14 the pinch roller P is coupled directly to the motor shaft to engage the tape T. The motor shaft extends past the pinch roller P to the slip torque clutch C, with the flywheel I then being mounted for rotation above the clutch C.

As is evident from the different embodiments illus trated in FIGS. 11, 12 and 14, the invention may be carried out in various constructions. The flywheel or other inertial load should be connected to the synchronous motor directly or indirectly with the aid of the slip torque clutch. If necessary, a speed reducer could be used at some point in the coupling chain between the motor and the load or the flywheel without changing the manner of operation.

1 claim:

1. Apparatus for applying rotational driving torque to a load including in combination:

a rotational load having predetermined inertia and presenting a first greater driving torque as said load is brought to an opening speed, and requiring a second lesser driving torque to maintain rotation of said load at the operating speed; a synchronous motor having an output shaft and capable of producing said second driving torque at its synchronous operating speed, said motor being incapable of producing said first greater driving torque at a speed below its synchronous speed and failing to rotate when a load requiring such greater torque is applied; and a slip torque clutch having a hollow cylindrical clutch drum and a clutch spring in engagement with the inner surface of said clutch drum, said spring resiliently urged outwardly into frictional contact with the inner surface of said drum for rotation therewith and including at least one projection thereon a clutch shaft aligned with the axis of said clutch drum and carrying therewith a lever for engagement with said projection, said clutch drum connected for rotation with one of the output shafts of said motor and said rotational load and said clutch shaft connected with the other of the output shaft of said motor and said rotational load, and wherein the torque at which said clutch slips is selected to be less than the first greater driving torque which would prevent said synchronous motor from rotating upon initial energization.

2. The combination according to claim 1 wherein said projection extends from said spring inwardly into the space inside said clutch drum.

3. The combination according to claim ll wherein said clutch drum is connected with the output shaft of said motor and said clutch shaft is a drivenshaft connected with said load.

4. The combination according to claim 1 wherein said spring is bent into an arcuate shape to conform with the inner surface of said clutch drum and both ends thereof are bent inwardly to form first and second projections extending toward the axis of said clutch drum cylinder, the force exerted by said spring upon the inner surface of said drum establishing the torque at which said clutch slips by relative slippage between said spring and said drum. 

1. Apparatus for applying rotational driving torque to a load including in combination: a rotational load having predetermined inertia and presenting a first greater driving torque as said load is brought to an opening speed, and requiring a second lesser driving torque to maintain rotation of said load at the operating speed; a synchronous motor having an output shaft and capable of producing said second driving torque at its synchronous operating speed, said motor being incapable of producing said first greater driving torque at a speed below its synchronous speed and failing to rotate when a load requiring such greater torque is applied; and a slip torque clutch having a hollow cylindrical clutch drum and a clutch spring in engagement with the inner surface of said clutch drum, said spring resiliently urged outwardly into frictional contact with the inner surface of said drum for rotation therewith and including at least one projection thereon, a clutch shaft aligned with the axis of said clutch drum and carrying therewith a lever for engagement with said projection, said clutch drum connected for rotation with one of the output shafts of said motor and said rotational load and said clutch shaft connected with the other of the output shaft of said motor and said rotational load, and wherein the torque at which said clutch slips is selected to be less than the first greater driving torque which would prevent said synchronous motor from rotating upon initial energization.
 2. The combination according to claim 1 wherein said projection extends from said spring inwardly into the space inside said clutch drum.
 3. The combination according to claim 1 wherein said clutch drum is connected with the output shaft of said motor and said clutch shaft is a driven shaft connected with said load.
 4. The combination according to claim 1 wherein said spring is bent into an arcuate shape to conform with the inner surface of said clutch drum and both ends thereof are bent inwardly to form first and second projections extending toward the axis of said clutch drum cylinder, the force exerted by said spring upon the inner surface of said drum establishing the torque at which said clutch slips by relative slippage between said spring and said drum. 